A conventional two wheeler, like a bicycle with two wheels arranged in a line, tends to sideslip when making a sharp turn, to drift during braking, and to lose balance and yaw when the two wheeler is initially started or moves slowly, thereby imposing potential danger to the rider. With two wheels mounted on one axle, a conventional three or four wheeler is more stable at a lower speed but it lacks dynamic movability and is hence unable to tilt while needed. Therefore, a frame mechanism is desired to eliminate those drawbacks mentioned above.